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RE: Fly ash in concrete

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We have had problems on some jobs because the finishers were not used to working with it and they would try to finish it the same as concrete with no fly ash.  The concrete would get sticky on them.  Once they got used to working with it, we have had no problems.  I have read that controlling air content in air-entrained concrete can be difficult with fly ash in the mix.  I believe it is a problem if the carbon content is too high.  I have also read that fly ash helps prevent scaling on exterior flatwork.  Typically I do not allow fly ash in air-entrained concrete.
 
Roger C. Davis
Architect
SDS Architects, Inc.
 
 
 -----Original Message-----
From: DWILLIAMSSEI(--nospam--at)aol.com [mailto:DWILLIAMSSEI(--nospam--at)aol.com]
Sent: Thursday, May 24, 2001 11:25 AM
To: seaint(--nospam--at)seaint.org
Subject: Fly ash in concrete

Has anyone had negative experiences with using fly ash in concrete mixes?

I'm working with an architect who doesn't want it used, but I'm not sure why.
 The spec's call for 3,500 psi 28 day strength concrete.  Fly ash is not
mentioned in the spec's, but a contractor has asked if it's permissible to
add it to the mix.  I understand that fly ash is used to improve flowability
of dry mixes.  I couldn't find much other information regarding the use of
fly ash in ACI 318 or any of my materials and concrete references.

The application for the concrete in question is spread footings for steel
columns and perimeter footings for slab/brick masonry support for a 2-story
building.

Thanks.

David Williams, P.E.
Snyder Engineering, Inc.
Columbia, MO